This application claims the priority of Korean Patent Application No. 2002-57565, filed Sep. 23, 2002 in the Korean Intellectual Property Office, which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an optical receiver in an optical communication system, and more particularly, to a method and an apparatus for optimizing a decision level of a signal output from an optical receiver to obtain a minimum bit error rate (BER) by measuring output characteristics of the optical receiver and adjusting a reference voltage of the optical receiver based on a measurement result.
2. Description of the Related Art
Optical signals transmitted through a plurality of optical amplifiers and a plurality of optical transmission lines are input to an optical receiver and converted into electric signals to be input to a clock and data recovery unit. In this process, the optical signals are compressed or dispersed due to dispersion and non-linear effects when passing through the plurality of optical transmission lines. In addition, natural emission noises are inserted to the optical signals while passing through the plurality of optical amplifiers, so noises are accumulated in level one of the optical signals. Thus, in order to determine whether the received optical signals are electrically level one or level zero while obtaining an optimum data characteristic, i.e., a minimum bit error rate (BER), in the clock and data recovery unit, the distribution of level one and level zero of electrical signals output from the optical receiver has to be controlled.
Here, a conventional optical receiver determines the level of an electric signal based on a fixed reference, so the conventional optical receiver cannot determine the level of the electric signal when the strength of the received optical signal or the eye diagram of the received optical signal is changed.